The mechanical ventilation of a patient considerably differs at times from a natural spontaneous breathing in terms of the pressures applied and the time course of the dispensing of the breathing gas. This may represent a burden for the patient. The maintenance and promotion of spontaneous breathing is therefore of increasing significance. The prior-art systems pursue, in general, two goals for promoting the spontaneous breathing, namely, to promote the spontaneous breathing breath by breath by mechanical pressure support and to train the patient to breath spontaneously, on the one hand. On the other hand, the spontaneous breathing shall be possible unhindered at any time during a pressure-controlled ventilation in order to achieve an improved ventilation or perfusion ratio thereby. It is essential in any case that the user sets machine parameters, which the patient can influence only partly if at all. In case of pressure-supported ventilation, the machine parameters set by the user are a suitable pressure value, while the inspiration time as well as a suitable pressure value are preset by the user in case of pressure-controlled ventilation.
It is often problematic, in case of pressure-supported ventilation, that, contrary to natural spontaneous breathing, tidal volumes that hardly differ from one another are obtained. A further development of conventional pressure support is variable pressure support. The value of the pressure support set by the user varies in this method [cf. Spiet, P. M. et al.; Effects of Different Levels of Pressure Support Variability in Experimental Lung Injury; Anesthesiology 2009; 110: 342-350].
Even though the tidal volumes applied vary in the course of ventilation according to this method, the corresponding change is achieved only based on a random principle, which has no recognizable relation to the physiological regulation of spontaneous breathing.
The user sets the inspiration time in patient-triggered, pressure-controlled ventilation. Methods in which the inspiration time may vary if spontaneous breathing efforts occur during the last quarter of the mechanical ventilation stroke are known in this connection (BiPAP; described in “Mini-Handbuch Dräger Beatmung, Beatmungsmodi and Funktionen kurz erklärt [Dräger Mini Handbook of Ventilation; Brief Explanation of Ventilation Modes and Functions], Version 1.1; p. 6; 2014).
The patient can trigger the switching into expiration prematurely by spontaneous breathing activity in this ventilation mode. However, the variance is achieved in this case comparatively randomly here as well, especially if the patient initiates the expiration time during the last quarter of the stroke. There is no recognizable relation to the physiological regulation of spontaneous breathing in this case, either.
Based on the above-described problems, there are efforts to improve the mechanical ventilation of a patient, and especially to carry it out more gently for the patient, with the use of EMG measuring units, which detect breathing efforts of the patient being ventilated on the basis of electromyographic signals.
A ventilation system for the non-invasive ventilation of a patient, in which the ventilation is controlled by means of EMG signals, is known in this connection from DE 10 2012 003 509 A1. It is essential for the technical solution being described that interfering ECG signal components are suppressed from the electrode signal generated by means of electrodes on the patient's thorax in order to obtain electromyographic signals (EMG signals) representing the breathing effort and to control the ventilation drive as a function of these EMG signals as accurately as possible.
Another device for automatically controlling a ventilation system is known from DE 10 2007 062 214 B3. A proportionally supporting ventilation of the lungs, of a patient being ventilated, is achieved by means of the ventilation system described. The EMG signal representing the patient's breathing activity is transformed, by means of a preset transformation rule, into a pressure signal, so that the mean deviation of the resulting pressure signal from the respiratory muscle pressure is minimized. The breathing effort pressure is determined in this case as a weighted mean.
It is, furthermore, problematic in the prior-art systems for the pressure-supported or pressure-controlled ventilation of a patient with reduced spontaneous breathing that changes in the breathing activity of the patient are taken into account for the control of the ventilation system, especially of the ventilator unit, either only insufficiently or at least with a great time delay. Another problem is often represented here by the fluctuating quality of the EMG signal, which is superimposed, on the one hand, by strong other electrical signals, for example, ECG signals, and is influenced, on the other hand, by the changing contacting of the electrodes on the thorax.